Effect of Reducing and Oxidizing Atmosphere on Photoluminescence of Undoped, Eu Doped and Dy Doped Nanostructured CaAl2O4

Abstract

Monocalcium aluminate (CaAl2O4) doped with Eu2+ is a phosphor that produces phosphorescence in the blue light (440 nm). It has attracting a great deal of attention because of its wide applications in energy-efficient illumination systems and information displays. CaAl2O4 codoped with Eu2+ and Dy3+ exhibits a very strong and long lasting persistence luminescence that could have many applications in the fields of emergency lighting signs, night-vision signage, in vivo bioimaging, dosimetry and optical data storage.In this work, we present the effect of the thermal treatment in the reducing (nitrogen) and oxidizing (air) atmosphere on the photoluminescence (PL) properties of nanostructured undoped CaAl2O4, CaAl2O4:Eu and CaAl2O4:Dy synthesized by the combustion method. The synthesized powders were characterized by XRD, SEM-EDS, FTIR and Raman techniques. The XRD analysis revealed that the powder mainly consists of krotite (CaAl2O4) together with a small amount of grossite (CaAl4O7) and mayenite (C12Al14O33).The 3D excitation-emission spectra of undoped and untreated CaAl2O4 exhibits a broad band with excitation/emission maximum at 338/412 nm, respectively. The thermal treatment slightly shift the position of the maximum for both the reducing and oxidizing atmosphere. It is interesting to note that the emission peak is red-shifted as the excitation wavelength red-shifts in the untreated sample while the emission peak positions are independent of the excitation wavelength in both reduced and oxidized samples. It is interesting to note that the emission peak shifts to red as the excitation wavelength shifts to red in the untreated sample, while the emission peak positions are independent of the excitation wavelength in reducing or oxidizing samples.The Eu doped sample treated in the oxidizing atmosphere exhibit the typical Eu3+ emission sharp bands while the reduced Eu doped sample reveals only broad Eu2+ emission band that partially overlaps with the band observed in undoped samples. The Dy doped samples exhibit the typical Dy3+ emission sharp bands regardless of their reducing or oxidizing thermal treatment.